This invention relates to a voltage protection and biasing circuit and more particularly, to a circuit which allows voltage to be provided to a terminal of a transistor, effective to operatively bias the transistor while concomitantly protecting the transistor from damage which is caused by transient voltage surges or xe2x80x9cspikesxe2x80x9d.
Transistors, such as and without limitation field effect transistors, are used in many assemblies and/or devices to control the application or communication of electrical voltage to a component which is oftentimes referred to as xe2x80x9cthe loadxe2x80x9d. For example, in vehicles, a device, such as a switch, is used in combination with a field effect transistor to selectively couple and/or communicate the voltage which emanates from the vehicle battery to a component or load, such as an interior convenience lamp or window activation motor. Particularly, the switch or device selectively biases or allows voltage to be applied to the gate terminal of the field effect transistor, effective to allow battery voltage to be communicated to the component or load through the source and drain terminals of the transistor.
While this arrangement adequately allow s the battery voltage to be selectively communicated to the component or the load, it suffers from some drawbacks. Particularly, the field effect transistor, in this arrangement, is typically biased by use of the vehicle battery (i.e., the battery voltage is selectively applied and/or communicated to the gate terminal of the field effect transistor) During periods of relatively high transient battery voltage surges, xe2x80x9cspikesxe2x80x9d, or increases, the biasing voltage damages, destroys, or xe2x80x9cpunches throughxe2x80x9d the field effect transistor, thereby requiring repair and replacement of the transistor, undesirably increasing the overall vehicle maintenance costs, and potentially causing surge type damage to the other components of the vehicle. Typically, the load or component is protected against such xe2x80x9cspikesxe2x80x9d in one of several conventional and known manners.
Some circuit configurations are used to address this drawback. For example, a voltage divider circuit is typically coupled between the vehicle battery and the field effect transistor and is effective to reduce the amount of biasing voltage which is communicated and/or coupled to the gate terminal of the field effect transistor. However, the amount of such voltage reduction is limited by the amount of voltage which is required to be communicated to the field effect transistor in order to operatively bias the transistor. Hence, while this voltage reduction approach and circuit configuration is effective to protect the field effect transistor from some relatively small transient voltage increases or surges, it does not typically provide protection against large transient voltage increases.
Zener diodes are also connected to the vehicle battery and to the field effect transistor and are somewhat more effective to protect the field effect transistor against transient voltage increases or surges. However, these zener diodes are relatively costly and undesirably increase the overall complexity of the circuit.
There is therefore a need for a new and improved circuit to bias and protect a field effect transistor while concomitantly allowing a biasing voltage to be selectively coupled to the field effect transistor, thereby allowing the operatively biased field effect transistor to couple voltage from a battery to a component or a load.
It is a first object of the present invention to provide a new and improved circuit to bias and concomitantly protect a transistor against transient voltage increases or xe2x80x9cspikesxe2x80x9d.
It is a second object of the present invention to provide a new and improved circuit to generate an electrical signal which has a certain first value which remains substantially constant as the battery produces voltage signals of varying voltage values.
According to a first aspect of the present invention, a circuit is provided for use in combination with a battery which is adapted to selectively generate a voltage, a component which is to selectively receive the voltage, and a field effect transistor which has a source terminal which is coupled to the battery, a drain terminal which is coupled to the device, and a gate terminal which selectively allows the voltage to be communicated from the battery to the component through the source and drain terminals. The circuit includes a substantially constant electrical current source; and a resistor which is coupled to the substantially constant electrical current source and which cooperates with the substantially constant electrical current source to provide a substantially constant amount of biasing voltage to the field effect transistor.
According to a second aspect of the present invention, a method is provided for allowing electrical voltage to be communicated from a battery to a device, the voltage varying between a first low value and a second higher value. The method including the steps of providing an electrical component which allows the electrical power to be communicated from the battery to the device when the electrical component receives an electrical signal having a certain value; creating the electrical signal; communicating the electrical signal to the electrical component; causing the communicated electrical signal to have and maintain the certain value when the voltage varies between the first low value and the second high value.
These and other aspects, features, and advantages of the present invention will become apparent from a reading of the following detailed description of the preferred embodiment of the invention and by reference to the following drawings.